Packet transmission services have continuously gained in importance in mobile communications. Such services include the SMS (Short Message Service), first introduced in the GSM (Global System for Mobile Communications) protocol, and TCP/IP (Transmission Control Protocol/Internet Protocol) services. More details of these services are described in the book by M.-B. Pautet: The GSM system for mobile communications, published by the authors, ISBN 2-9507190-0-7, 1992; and in M. Rahnema: Overview of the GSM system and protocol architecture, IEEE Communications Magazine, vol. 31 (April 1992) no. 4, pp. 92-100.
In mobile communications, one example of a packet transmission service which has had tremendous economic success is the SMS used both in GSM and in GPRS (General Packet Radio Service) mobile communications networks. Principles of the SMS are described in G. Brasche, B. Walke: Concepts, services, and protocols of the new GSM phase 2+ general packet radio service. IEEE Communications Magazine, vol. 35 (August 1997) no. 8, pp. 94-104.
As it pointed out in J.-H. Park: Wireless internet access for mobile subscribers based on the GPRS/UMTS network, IEEE Communications Magazine, vol. 40 (April 2002) no. 4, pp. 38-49, a sustained high Quality of Service (QoS) level is mandatory and insisted upon by the senders of the messages. In order to enable the deployment of the packet transmission services like SMS in professional environments, it is necessary to define and maintain a pre-determined level of reliability for the packet transmission services and also to define and maintain attributes relating to precedence of packet transmission services as well as for the delay of the packet transmission service.
Unfortunately, sustained high QoS levels can usually not be guaranteed for the SMS transmission service, and SMS Centers therefore cannot currently provide the high service quality in all cases. In particular, the provision of the SMS suffers from packet losses, produced by e.g. time-outs, entailing forced packet deletions. These forced packet deletions are the consequences of protocols in the signalling domain of the infrastructure of a mobile communications network, including the Base Station System Application Part+ (BSSAP+) and the Mobile Application Part (MAP) protocols (this is discussed in J.-H. Park: Wireless internet access for mobile subscribers based on the GPRS/UMTS network. IEEE Communications Magazine, vol. 40 (April 2002) no. 4, pp. 38-49). The time-outs occur for various reasons, disturbances and network errors or obstacles, leading to failures in the delivery of the packets. For instance, when an origin terminal (i.e. the point of origin of the packet) and a destination terminal (such as the mobile station which can be for example a mobile phone or a data card) are subscribed to different network operators and the different network operators do not have a roaming agreement between them.
When the SMS is used for non-professional, i.e. private, communication from one subscriber to another subscriber, the lack of sustained high QoS levels may be acceptable. However, this is no longer the case for the deployment of SMS in professional scenarios.
In order to reduce the effect of packet losses and, hence, to improve the quality of the packet transmission service, a quantitative analysis of the QoS in the signalling domain can be carried out. To date, only a few QoS parameters have been defined by the standards bodies. The existing QoS parameters monitor the transmission quality only and cover only mobile-originated and mobile-terminated SMS. The existing QoS parameters do not cover transmissions to or from fixed line stations. The definitions of the QoS parameters are tailored for the end-to-end transmissions and include delivery time and completion rate as QoS parameters. The definitions are given in ETSI: Digital cellular telecommunications system (Phase 2); Mobile Application Part (MAP) specification (GSM 09.02 version 4.19.1) ETS 300 599 December 2000, and in ETSI: Speech processing transmission and quality aspects (STQ); QoS aspects for popular services in GSM and 3G networks; Part 2: Definition of quality of service parameters and their computation. ETSI TS 102 250-2 V1.2.1 (2004-06), June 2004.
Both A. Andreadis, G. Benelli, G. Giambene, B. Marzucchi. A performance evaluation approach for GSM-based information services. IEEE Transactions on Vehicular Technology, vol. 52 (2003) no. 2, pp. 313-325, and T. C. Wong, J. W. Mark, K.-C. Chua: Joint connection level, packet level, and link layer resource allocation for variable bit rate multiclass services in cellular DS-CDMA networks with QoS constraints. IEEE Journal on Selected Areas in Communications, vol. 21 (2003) no. 10, pp. 1536-1545, discuss the QoS parameters in their respective publications. The authors statistically model the packet traffic and present results on the related efficiency parameters.
To date the forced packet deletions mentioned above have not been taken into consideration. Furthermore, the existing QoS parameters (see the ETSI publications discussed above) do not completely fulfil the needs arising from a professional SMS.
Additional QoS parameters have been invented and described along with several measurement results in A. Waadt, G. Bruck, P. Jung, M. Kowalzik, T. Trapp, and C. Begall: A Reconfigurable QoS Monitoring Framework for Professional Short Message Services in GSM Networks. IEEE International Conference on Service Computing, vol. 2 (July 2005), pp. 22-29. These QoS Parameters can be measured within an SMS Center and in near real-time. A conceivable system framework for a QoS machine, controlling the QoS within a SMSC, is also described in this publication.
SMS Centers communicate with the infrastructures of service providers by using the SS7 (Signalling System 7) protocol, the additional QoS parameters consider the signalling domain explicitly. The additional QoS parameters have been applied to SMS in real GSM networks. To quantify the corresponding QoS levels, the signals and error acknowledgements, made available through the SS7 protocol, need to be calculated. These signals and error acknowledgements also cover SMS related services, which use signals from the MAP of the SS7 protocol.
Due to its popularity, roaming agreements for packet transmission services between network operators have been established all around the world. However, in some areas SMS roaming can sometimes be difficult. Quite often, small network operators are faced with numerous problems in establishing roaming agreements with larger network operators. Voice telephone calls between different mobile communications networks into foreign countries can be routed through the ISUP (ISDN User Part) using a fixed telephone network. However, the provision of SMS services requires roaming agreements between the network operators. That is the reason for scenarios in which customers are able to phone mobile stations, such as mobile telephones or personal digital assistants, in foreign countries, but are unable to use packet transmission services to the same mobile station. Currently, there are long waiting lists for the small network operators who want to establish roaming agreements with the major network operators. The major network operators are often unwilling to establish these roaming agreements because they fear an unwieldy number of roaming agreements. As a result there are restrictions in the service accessibility for packet transmissions, such as SMS services.
Together with the SMS service in the GSM protocol, there are other packet switched services which have sprung up in the last years and which are having similar compatibility problems like the SMS services. An example is found in North America in which the IS41 and IS95 protocols are used in TDMA (Time Division Multiple Access) and CDMA (Code Division Multiple Access) networks (e.g. CdmaOne, Cdma2000).
Even providers of the popular Instant Messaging (IM) Services (e.g. ICQ, MSN Messenger, IRC or AIM) are beginning to connect their IM networks, in order to get over the obstacles of communication restricting incompatibility. Currently there are many different protocols used by the different IM providers. Some of the most important protocols include Jabber (XMPP), whose protocol is an accepted internet standard, and SIP (Session Initiation Protocol), which is created by the IETF (Internet Engineering Task Force) and popular for its packet switched telephoning use (“voice over IP”).
The above-mentioned services use central mapping servers, which provide status and routing information to the different devices, mobile stations (MS), etc. (collectively called service clients). To be reachable, the service client notifies the central mapping server about its status and location, when the service client is turned on or changes its address. When the service client, that wants to initialize a connection with a target device, has the requested routing information from the central mapping server, the service client is able to connect to the target device directly through a network, without further detour over the central mapping server or another server.
In the case of a GSM network, a Home Location Register (HLR) provides the functionality of the aforementioned Mapping Server. The stored information about the mobile station (service client), are the IMSI (International Mobile Subscriber Identity) of the mobile station and its last known status or address, if the mobile station is reachable. This address is the global title (GT) of the Mobile Switching Center (MSC) which is connected with a base station having a radio link to the mobile station. The GT of the MSC (the MSC-GT) is routing information to that MSC and therefore routing information to the mobile stations which are located in the NSS (network and switching subsystem) of that MSC.
A SMS Center (SMSC) in a GSM network uses only three MAP primitives of the SS7 protocol to transmit short messages. Every command delivers a status report. The interpretation of these status reports at the SMS Center facilitates the generation of various error codes, including the acknowledgement of the successful delivery of the SMS.
It is possible for a service subscriber to change its subscription and thus its home network from a first network operator OP1 to a second network operator OP2. The service subscriber is generally able to keep his old called party address or MSISDN (Mobile Station Integrated Services Digital Network) number when changing—this is known as porting the MSISDN. Usually the mapping server (HLR) of the mobile station, which was ported from the first network operator OP1 to the second network operator OP2, is located in the second network OP2.
Suppose now that a sender wishes to send an SMS to the service subscriber of the ported mobile number. The sender is subscribed to a message originating operator (OP). This message originating operator has roaming agreements with the first network operator OP1 which is the number range holder of the MSISDN of the ported mobile number. As long as the message originating operator also has a roaming agreement with the new home operator (second network operator) OP2 of the service subscriber, no problems occur: In order to retrieve routing information to the destination subscriber (here: the ported mobile number), the message originating operator (OP) will send a MAP command, querying for routing information, to the number range holder of the called party address, the MSISDN of the destination subscriber. This number range holder is the first network operator OP1. If, as usual, the mapping server or HLR, which is responsible for the ported destination subscriber, is located in the second network OP2, a Signalling Relay Function for support of Mobile Number Portability (MNP-SRF) of OP1 will forward the querying MAP command to OP2. The mapping server (HLR) of OP2 responsible for the ported destination subscriber will answer the query with an acknowledging signal, which is sent to the message originating operator (OP). If, however, the message originating operator OP has no agreement with the first network operator (number range holder) OP1, no communication between the message originating operator OP and the first network operator OP1 is possible. On the other hand, if the message originating operator OP has an agreement with the first network operator OP1, but no agreement with the second network operator OP2 (and now home network of the service subscriber), the acknowledging answer from the mapping server (HLR) of OP2 will not reach the origination operator (OP), due to the absence of roaming agreements between OP and OP2. The message originating operator OP does not get any answer as to the sent MAP command and may only guess the reason.
Several patents and applications are known which address the problem of improving the service between mobile communications networks.
US patent application 2005-0124302 (Yoon et al.) teaches a method to improve the service within wireless systems which collaborate. The HLR information is periodically updated and synchronized through interfacing between the wireless network systems.
The U.S. Pat. No. 6,832,089 (Nilcom) teaches a method which addresses the problem of number portability or incomplete number plans within the same country. A computer with SS7 connections is used as an SMSC relay to relay the short messages sent by an operator OP to a subscriber of a first network OP1 visiting a second network OP2, OP2 having no roaming agreement with the network OP. The SMS is sent with the global title GT of the visited MSC to a companion SMSC in a network which does have a roaming agreement with the second network OP2. The computer is capable of interrogating all of the HLRs of the country in which the number portability is operated. A database is built in a cache memory of the computer for all the mobile subscribers of the country in which the portability is operated so that the computer will know which HLR to interrogate, without searching, once the HLR has been found a first time.
The U.S. Pat. No. 6,512,926 teaches a dynamic routing system for transmission of SMS. A numbering plan contains the numbers of the short message transmission centers (SMSC) and the possible interconnections between the different SMSCs and the switching centers (MSC) of the networks of the called mobile telephone. A numbering plan manager defines from the number of the called party the relay transmission center or centers (SMSC) in order to reach the switching centre (MSC) visited by the intended recipient of the short message (SMS).
Various approaches to improve the delivery of SMS between different network providers have been suggested in the prior art. However, none of the known approaches teaches a system or a method which allows a reliable, high quality of service for data packet transmission in an environment with several different network operators without roaming agreements. These operators can be possibly located in different countries.